Unbending connects sea level to faulting at fast-spreading mid-ocean ridges

Abstract

Topographic spectra of abyssal hills from fast-spreading mid-ocean ridges have concentrations of power at Milankovitch frequencies and, in particular, around 1/(41 ka) [1].  This frequency corresponds to variations in Earth’s obliquity and is prominent in many climate records, including Pleistocene sea-level variations. Sea-level variations are understood to induce variations in magma supply to the ridge axis [2]. How might these magma-supply variations pace the faulting that creates abyssal hills?  We hypothesise that magma-supply variations introduce a perturbation to elastic plate thickness that is correlated with crustal thickness [3]. Building on Roger Buck’s theory for plate unbending and faulting at fast-spreading ridges [4], we show how thickness perturbations lead to concentrations in bending stresses in thinner parts of the plate.  These concentrations can be significant relative to background unbending stresses and may therefore pace faulting, depending on their amplitude and wavelength.  Using perturbation analysis and numerical solutions of Euler-Bernoulli beam theory, we develop predictions for fault spacing as a function of spreading rate, amplitude of magma supply variations, and other physical parameters.[1] Huybers, Peter, et al. "Influence of late Pleistocene sea-level variations on mid-ocean ridge spacing in faulting simulations and a global analysis of bathymetry." PNAS https://doi.org/10.1073/pnas.2204761119 [2] Cerpa, Nestor G., David W. Rees Jones, and Richard F. Katz. "Consequences of glacial cycles for magmatism and carbon transport at mid-ocean ridges." EPSL https://doi.org/10.1016/j.epsl.2019.115845 [3] Boulahanis, Bridgit, et al. "Do sea level variations influence mid-ocean ridge magma supply? A test using crustal thickness and bathymetry data from the East Pacific Rise." EPSL https://doi.org/10.1016/j.epsl.2020.116121 [4] Buck, W. Roger. "Accretional curvature of lithosphere at magmatic spreading centers and the flexural support of axial highs." JGR https://doi.org/10.1029/2000JB900360